Emergency drain



Aug. 5, 1958 L. v. LARSEN EMERGENCY DRAIN Filed Aug. 23, 1955 5 Sheets-Sheet 1,

1958 4 L. v. LARSEN 2,846,109

EMERGENCY DRAIN Filed Aug. 23, 1955 5 Sheets-Sheet 2 w a 77rve%% 1/ Q76 7/Z 37156 6 1958 L. v. LARSEN 2,846,109

EMERGENCY DRAIN Filed Aug; 25, 1955 5 Sheets-Sheet s 5, 1958 I 1.. vfLARsEN 2,846,109

EMERGENCY DRAIN Filed Aug. 23, 1955 5 Sheets-Sheet 4 5, 1958 L. v. LARSEN 2,846,109

' EMERGENCY DRAIN Filed Aug. 25, 1955 5 Shgeps-Sheet 5 United 12 Claims. (Cl. 226-26) This invention relates to a self-operating emergency drain, and is particularly well adapted for use on floating roofs installed in oil storage tanks.

Oil storage tanks having floating roofs are used for the storage of liquid petroleum products of relatively high volatility, such as sour crude oils, natural gasolines and the like. A floating roof is a steel structure which floats upon the surface of a liquid stored product and rises and falls as the level of the product in the tank rises or falls.

Such floating roofs must be capable of supporting considerable amounts of snow and rain which may accumulate on them. They are usually provided with means for draining accumulated water. A commonly used draining means is a hand-operated valve which, when opened, permits the accumulated water to flow out through a hose or pipe drain without coming into contact with the stored product. One of the difliculties with this arrangement, however, is that when it is the sole means for draining a roof, the failure of a maintenance crew to open it at a critical time may result in sinking of the roof through structural failure or loss of buoyancy. In such cases, a dangerous condition results from the exposure of highly flammable products to the atmosphere. Also, much of the product is lost.

It is, therefore, desirable to provide an emergency overflow drain on floating roofs, so that if a regular drain for some reason fails to operate, the emergency overflow drain goes into use as soon as the level of water on top of the floating roof reaches a dangerous point. Such an emergency drain permits the accumulated water to flow down into the stored product and to accumulate in the tank, usually at the bottom. This emergency drain is particularly useful when the stored product is immiscible with water or only slightly miscible.

I have invented a new type of emergency overflow drain which is completely self-actuating, does not require priming, does not require the maintenance of a liquid seal and always goes into operation when water accumulation reaches a critical stage at which time it should he removed to eliminate danger to the roof.

My invention comprises a drain having two standpipes, the first of which is open at its lower end to the stored product below the roof or membrane and the second being open at its lower end to liquid (water) on top of the tank, the upper end of the second standpipe intercommunicating with the first standpipe and both standpipes being vented to the atmosphere from above the area of intercommunication between the standpipes.

The principle of operation of my invention is based upin the differences in specific gravity between water and the stored product, and my invention is designed to function when the stored liquid under the roof is of lesser specific gravity than that of the water accumulated on top of the roof.

My invention and its operation will be described with ice of Figure 2, showing a central sump in the floating roof I and a manually-operated drain and the emergency drain of my invention in the sump. In this view the roof is floating on the liquid product and there is no water accumulated on top of the roof;

Figure 4 is the same view as Figure 3, except that a quantity of water has accumulated on top of the roof at an intermediate level between the surface of the roof and the critical depth;

Figure 5 is the same view as Figure 3, except that the water accumulated on top of the roof has reached the critical level;

Figure 6 is the same view as Figure 3, except that the water level has been drawn down from its critical level;

Figure 7 is the same view as Figure 6, except that the water level has continued to be lowered;

Figure 8 is a cross-sectional view of another embodiment of my invention;

Figure 9 is a cross-sectional view of a third embodiment of my invention; and

Figure 10 is a cross-sectional view of a fourth embodiment of my invention.

In Figure l the floating roof in tank 10 is provided with a peripheral portion 11 consisting of pontoons and a central single deck portion 12 sloping generally toward the center. A central sump 13, being generally lower than any portion of the single deck 12, contains-a hose or pipe drain 14, and also contains an emergency overflow drain 15.

Figure 2 is a cross-sectional view of Figure 1 and shows the roof floating on a liquid in the tank. It also shows the general relationship of the conventional manual drain to the roof and tank in addition to the emergency drain positioned in the sump. 7

Referring nowto Figure 3, one type of emergency overflow drain 15 consists of a standpipe 16 open-at its lower end 17 to the stored product, another standpipe 18 open at its lower end 19 to the sump 13 and a portion 21 interconnecting the standpipes at their upper ends. Vent 20 originates at the interconnecting portion and leads to the atmosphere; it is high enough to prevent water flowing in or the product out through it. Trap 22 is provided to prevent the product from flowing out into the sump 13 or onto the deck portion and has an opening 23 at its lower end to permit water to flow into the standpipe It).

The operation of my invention is shown progressively in Figures 3, 4, 5, 6 and 7.

In Figure 3 the floating roof is floating on the product without any water on the deck. The level of the product 24 in the standpipe 16 is the free liquid level of the product, being slightly above the level of the deck 12 because of the displacement of the product caused by the weight of the floating roof.

In Figure 4 water 25 has accumulated on the deck, filling and rising above the sump 13. The water in the trap 22 has risen to the same level as the water on the deck, and water 25 has also risen in the standpipe 18. In this way the product which flows first from standpipe 16 into standpipe 18 is blocked from escaping due to the water barrier in the lower limits of standpipe 18. this figure, the water level has risen sufliciently high that the level of the product 24 in the standpipe 16 has risen above the level of the interconnection 21 between the two standpipes, so that a certain amount of product 24 has overflowed into standpipe 18.

As water continues to accumulate on the floating roof, the level rises to a critical point as shown in Figure 5. This critical point is established by computation as that level of water which the roof can support without exceedlng the allowable design stresses, and the emergency drain is so designed that the interconnection between the two standpipes permits water to begin draining off when the level of the water on the roof reaches the critical point. In Figure 5 the level of water 25 in standpipe 18, has reached the level of the interconnection 21 between the two standpipes, while the level of the stored product 13 has risen up the vent 2G commensurately. The water then begins to overflow at the interconnection 21, from standpipe 18 into standpipe 16. It flows down standpipe 16 into the stored product 24, and the level of water on the roof, therefore, remains constant, even though ram may continue to fall, until such time as the drain valve onthe outside of thetank at the lower end of the hose orpipe drain 14 is opened, permitting the water to flow off the roof.

In Figure 6 the valve has been opened and water has drained out through the drain 14 below the critical level. As this occurs, the levels of the two liquids in the two standpipes are reduced, and a certain amount of stored product 24 flows from the interconnection 21 down into standpipe 18, being always above the level of the water 25 in the standpipe 18.

It is desirable to prevent the stored product from flowmg out into the sump and thus create a fire hazard. Figure 7 shows the action of the trap 22 in catching and retaining the small amount of stored product 24 which falls in standpipe 18 as water is removed. This small ignount of stored product is removed through the drain Figure 8 shows a second embodiment of my invention, in which the operation is substantially identical to that described above. The product standpipe 26 is open at the top and the bottom open end 30 goes into the product. A larger water standpipe 27, also open at the top, is located concentrically to the product standpipe so that there is an interconnection between the two at 28. The water standpipe has an opening 31 at the bottom about at the bottom of the sump. Thus, as the level of water 25 on the roof and in the water standpipe 27 rises, so also does the level of the stored product 24 in the product standpipe 26. In Figure 8, the level is such that the product 24 has risen to the top of the product standpipe 26 so that it is about to overflow at the interconnection 28 into the water standpipe 27. As water continues to rise, the level of the Water will reach the interconnection 28, the stored product will have risen into the upper end 29 of the water standpipe, and water will flow from the water standpipe 27 through the interconection 28 into the product standpipe 26 and down into the product to the bottom of the tank. As Water is drained off through the valve and drainpipe 14, the level of liquids in the two standpipes falls but, as in the previous embodiment, a certain amount of product comes down the water standpipe 27.

Figure 9 shows a third embodiment of my invention in which the interior of the water standpipe 32 remains dry until the water 25 reaches a pro-level somewhat below the critical level. At the pre-level, water flows in 36, into pipe 35 and up 32. A water barrier is thereby formed against passage of product when it rises up 33 and spills over into 32. This is eifected by product standpipe 33 having a lower end 34 open to the product 24 below the roof and an upper end joined to the Water standpipe at the upper end of the latter. The lower end of water standpipe 32 is joined to a returning standpipe 35 which has an open end 36 at the prelevel to which water is allowed to accumulate before a water barrier in 32 forms. The valve then operates as does the embodiment of Figure 3 except that water and some product are retained in pipes 32 and 35' after the main drain 14 is opened.

Figure 10 shows another embodiment in which the interior of the water standpipe 38 remains dry until sometime before the water level reaches the critical point. By reference to Figure 10 it will be seen that product standpipe 39 has a lower open end 40 below the roof and in the product and an upper end in intercommunication with water standpipe 38 to form joining area 41 above which vent 42 protrudes to a height above the level to which the product rises when water accumulates on the roof before it is drained. The lower end 43 of water standpipe 38 is open and intercomrnunicates with the trap or return pipe 44. The bottom 45 of pipe 44 is closed and extends below the bottom of the sump in this embodiment although it need not do so. Similarly the return area 46 in Figure 9 need not be below the sump.

In all of the embodiments of my invention, the vertical dimensions of the various portions of the drain depend upon the height of water that may be seafely carried by the roof and upon the difference between the specific gravity of water and that of the stored product. By way of example only, I am setting forth below a representative emergency drain based upon certain stated operating conditions.

Example A typical 134 ft. diameter floating roof under which was stored a 49 lb. per cubic ft, product was tested by loading it with all of the water it could carry within the allowable design stresses as shown in Figure 5. The depth of water at the center of the 116 ft. diameter single deck portion was 2.11 ft. and the free product surface under this load was 0.32 ft. above the free Water surface.

An emergency overflow drain of the type of Figures 3-7 was designed for this roof based upon the specific gravity above mentioned. In this drain, with reference to Figure 5, h,,,=2.ll ft, e=0.32 ft. and h =2.43 ft., where h =the height of the water above said roof (critical level) at which it is desired that said drain become self-actuating, where e=the free product surface above the water surface at the critical level, and where h =the height of the product when the water level above the roof is at h The location of the overflow point, h must be determined by using these dimensions together with the weight of water, W at 62.4 lb. per cubic ft, and the weight of the product, -W at 49. lb. per cubic ft.

At the time water flows out the drain, the pressure of the water and the product above the overflow point must be the same. By considering a unit area, this can be expressed as w( w o) p( p o) This can be rearranged to become For this particular roof In addition to the overflow point, the depth of the sump must be determined. When the product overflows into the water leg, as shown in Figure 4, there must be a suflicient depth of water present to retain the product in the water leg. The equation for the equilibrium condition at the water-product interface is center deck plates adds to the weight of the water on the deck, the relative location of the product and Water a surfaces can be found. The weight of the center deck plate is equal to .125 ft. of water, so

Through rearrangement and substitution for W h this becomes In practice, the water leg and the sump are extended below the critical point a slight distance.

What is claimed is:

1. The combination of a self-actuating overflow drain mounted upon a floating roof storage tank adapted to drain excessive accumulations of water from said roof through said drain into a stored product of a specific gravity less than water beneath said roof, the drain having: a standpipe open at its lower end to said water on said roof and at its upper end to the atmosphere, a second standpipe extending through said roof and open at its lower end directly to said stored product and at its upper end to the atmosphere, said standpipes being interconnected near their upper ends for controllable interchange of the liquids between the standpipes.

2. The combination of claim 1 in which the drain is mounted in a sump located on said roof.

3. The combination of claim 1 in which the drain has dimensions are such that h is not less than and h is not less than W h' W h' where h =the height above said roof of the interconnection between the standpipes; h =the distance below said roof to the bottom opening of said first standpipe; h =the height of said water above said roof at which it is desired that said drain become self-actuating; h =the height of said stored product in said second standpipe when the water level above said roof is at h h,,=the height above said roof of said stored product in said second standpipe when it overflows into said first standpipe; hw=the height of said water above said roof when the product level above said roof equals h W =the unit weight of said water; W =the unit weight of said stored product.

4. The combination of claim 1 in which the said standpipes have a common upper end vented to the atmosphere above the interconnection between them.

5. The combination of claim 1 in which the first said standpipe extends at its lower end through said roof, turns and extends upwardly again through said roof.

6. The combination comprising a self-actuating emergency drain mounted essentially on the upper side of a membrane floating upon a liquid of comparatively low specific gravity to drain liquid of comparatively high specific gravity contained on the upper side of the membrane into the lower liquid, said drain having a first standpipe supported on said membrane, said first standpipe having at least one opening below the maximum level of high specific gravity fluid which the membrane can hold without sinking, a second standpipe supported on and extending through said membrane and open at its lower end to said lower liquid and in direct contact with the lower liquid, interco'mmunicating means from the upper end of the second standpipe to below the upper end of the first standpipe for controllable interchange of the liquids between the standpipes, said intercommunicating means effecting the interchange above the opening in the first standpipe and a vent to the atmosphere communi eating with at least one of said standpipes, said vent ex- 6 tending above the maximum height which the low spe cific gravity liquid reaches when high specific gravity liquid on the membrane flows through the second standpipe and into the low specific gravity liquid.

7. The combination of a self-actuating drain mounted upon a membrane floating upon a liquid of comparatively low specific gravity to drain liquid of a comparatively high specific gravity contained on the upper side of the membrane into the lower liquid, the drain having a first standpipe open at its upper end for receiving said upper liquid, a second standpipe extending through said membrane and open at its lower end directly to said lower liquid, a connecting pipe communicating with the bottom of the first standpipe and the upper end of the second standpipe, and a vent open to the atmosphere communicating with the second standpipe, the upper end of the first standpipe and the area of communication between the connecting pipe and the second standpipe being below the maximum level of high specific gravity liquid which the membrane can hold without sinking, said vent extending above the maximum height which the low specific gravity liquid reaches when high specific gravity liquid on the membrane flows through the second standpipe and into the low specific gravity liquid.

8. The combination of a self-actuating drain mounted upon a membrane floating upon a liquid of comparatively low specific gravity to drain liquid of a comparatively high specific gravity contained on the upper side of the membrane into the lower liquid, the drain having a first standpipe having an opening at its lower end for receiving said upper liquid, a second standpipe extending through said membrane and open at its lower end directly to said lower liquid, the second standpipe being interconnected to the first standpipe at their upper ends, an elongated vent open to the atmosphere extending upwardly from the area of interconnection, and a trap standpipe surrounding the first standpipe, the trap standpipe being open at its upper and lower ends, the lower end of the trap standpipe extending below the lower end of the first standpipe, the trap standpipe upper end and interconnection of the first and second standpipes being below the maximum level of high specific gravity liquid which the membrane can hold without sinking, said vent extending above the maximum height which the low specific gravity liquid reaches when high specific gravity liquid on the membrane flows through the second standpipe and into the low specific gravity liquid.

9. The combination of a self-actuating drain mounted upon a membrane floating upon a liquid of relatively low specific gravity to drain liquid of a comparatively high specific gravity contained on the upper side of the membrane into the lower liquid, the drain having a first standpipe having an opening at its lower end for receiving said upper liquid, a second standpipe extending through the membrane and open at its lower end directly to and in contact with said lower liquid, the second standpipe being inside the first standpipe and permitting passage of fluids between the standpipes, the height of the first standpipe being greater than the second standpipe and extending above the maximum height which the low specific gravity liquid reaches when high specific gravity liquid on the membrane flows through the second standpipe and into the low specific gravity liquid, the upper ends of each standpipe being open to the atmosphere, and the upper end of the second standpipe being above the opening in the lower end of the first standpipe.

10. The combination of a self-actuating drain mounted upon a membrane floating upon a liquid of comparatively low specific gravity to drain liquid of a comparatively high specific gravity contained on the upper side of the membrane into the lower liquid, the drain having a first standpipe having an opening at its lower end for receiving said upper liquid, a second standpipe extending through said membrane and open at its lower end to said lower liquid, the second standpipe being interconnected to the first standpipe at their upper ends, an elongated vent open to the atmosphere extending upwardly from the area of interconnection, and a trap standpipe around the first standpipe, the trap standpipe' being open at its upper end and closed at its lower end, the closed end of the trap standpipe extending below'the open lower end of the first standpipe, the upper end of the trap standpipe and interconnection of the'first' and; second standpipes being below the maximum level of high specific gravity fluid which the membrane can hold without sinking, said vent extending above the maximum height which the low specific gravity liquid reaches" when high specific gravity liquid on the membrane flowsthrough the second standpipe and into the low specific gravity liquid.

11. The combination of'a self-actuatingdrain mounted upon a membrane floating upon a liquid of comparatively low specific gravity to drain liquid of a comparatively high specific gravity contained on the upper side of the membrane into the lower liquid, the drain having a first standpipe having arr opening at its lower end for receiving saidupper liquid, a second standpipe extending through said membrane and open at; its lower end directly to said lower liquid, the second standpipe being interconnected to the first standpipe at their upper ends, an elongated vent open to the atmosphere extending upwardly from the area of interconnection, the interconnection of the first and second standpipes being below the maximum level of high specific gravity liquid which the membrane can held without sinking, said vent extending above the maximum height which the low specific gravity liquid reaches when high specific gravity liquid on the membrane flows through the second standpipe and into the low specific gravity'liquid.

12. The combination of a self-actuating drain mounted upon a membrane floating upon a liquid of comparatively low specific gravity to drain liquid of a comparatively high specific gravity contained on the upper side of the membrane into the lower liquid, the drain having a first standpipe having an opening at its lower end for receiving, said upper liquid, at second standpipe extending through said membrane and open at its lower end direct- .y to said lower liquid, the second standpipe being interconnected to the first standpipe at their upper ends, a ventopen to the atmosphere extending upwardly from the area of interconnection, and a trap standpipe surrounding the first standpipe, the trap standpipe being open at its upper and lower ends, the interconnection of the first and second standpipes being below the maximum level of high specific gravity liquid which the membrane can hold Without sinking, said vent extending above the maximum height which the low specific gravity liquid reaches when high specific'gravity liquid on the membrane flows through the second standpipe and into the low specific gravity liquid.

References Cited in the file of this patent UNITED STATES PATENTS 1,574,013 Wiggins Feb. 23, 1926 1,874,726 Wiggins Aug. 30, 1932 2,102,299 Wiggins Q Dec. 14, 1937 2,297,985 Rivers Oct. 6, 1942 2,359,416 Hammeren Oct. 3, 1944 UNITED STATES PATENT OFFICE Certificate of Correction Patent No. 2,846,109 August 5, 1958 Lyle V. Larsen It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1, line 66, for upin read up0n-; column 2, line '7, for jn read -in-; column 3, lines 53 and 54, for lnterconeotlon read 1nterconnect1on-; column 4, line 20 for seae1 read safel column 5 llnes 33 to 37 should a ear as shown below 0 I r instead of as in the patentm L h W hvh -W and h is not less than W,,h W h Co i) Signed and sealed this lfith day of December 1958.

[SEAL] Attest:

KARL H. AXLINE, Attestz'ng 0775067".

ROBERT C. WATSON,

Commissioner of Patents. 

